This study aims at reorganizing theories related to cross-border regional cooperation reflecting upon the reality of Northeast Asia. Case studies are conducted to analyze the factors behind the success or failure of cross-border cooperation in Northeast Asia. The study also intends to provide relevant strategic frameworks to promote future cooperative regional development in Northeast Asia. To achieve these objectives, Chapter 2 discusses the relevance of conventional regional theories in relation to the role and meaning of national border. Considering the fact that national borders still have significant effects in cross-border relations in Northeast Asia, theories of international cooperation are also included for review. National borders have different implications depending on the openness of the border. First, the border has a function of barrier. Second, it functions as a filter when a country opens up its border. Third, as border opening deepens, the border plays a role of connection and contact between different political and economic systems. We can imagine the borderless world in the distant future but not in the near future. Most regional theories assume homogeneous space ignoring borders and therefore are not adequate to explain the phenomena occurring by the border. As the globalization of economies intensifies, however, those theories based on the assumption of homogeneous space or functional space are gaining the explanatory power. International trade theories or cooperation theories employing the key concept of comparative advantage are still effective in explaining the scope and nature of cross-border cooperation. They are, however, not effective in explaining cross-border cooperation in small regions like the Tumen region. Strategic importance in a wider regional context counts instead of comparative advantages between component areas in a narrowly defined region. In other words, comparative advantage concept loses its relevance in small cross-border regions, while joint comparative advantage arising from cooperative arrangement of a cross-border region gains importance. Competitive advantage or new economic geography models provide relevant theoretical grounds for cross-border regions where factors of production freely move and inter-firm linkages are formed. These models have, however, limited applications where border barriers still exist and institutional compatibility across the border is not high. Arbitrage economy models and cross-border firm theories acknowledging the existence of border are useful in explaining cross-border interactions but they may nor hold explanatory power when the border gradually opens up. Chapter 3 reviews cross-border cooperation experiences in Europe and East Asia to draw reference points for cross-border regional cooperation in Northeast Asia. Assuming that regionalization (economic integration) will occur in Northeast Asia in the long-run as did in Europe, European experiences provide valuable lessons in both theoretical and policy terms. East Asian experiences, because of their similarities to Northeast Asia in an institutional context, offer more relevant examples for predicting the evolution of cross-border regional cooperation in Northeast Asia. The motives for cross-border cooperation in Europe include economic complementarity, resource polling, the economies of scale in providing public services and infrastructure, increasing flexibility of regional economies, and reducing transaction costs. Most of them apply also to the cases of Northeast Asia. More importantly, European experiences illustrate the importance of managing cross-border cooperation in addition to the motives. This study takes a detailed look at three examples of the Baltic region, the Transmanche, and the German-Polish border in order to draw lessons for the selected cases of Northeast Asia. (The rest is omitted)